1050 RADIATION BIOLOGY 



orient the reader; details may be found elsewhere. The experimental 

 animals were placed in cages arranged about a centrally located radium 

 source. The cages were placed at varying distances from the 2-g radium 

 source so that given daily doses were delivered during an 8- or a 24-hour 

 period of exposure. In Lorenz's original experiments (1946), continuous 

 exposure (24 hours per day) was used. The data from these early experi- 

 ments are available. Since more complete studies have been done using 

 8-hour daily exposures, only these later experiments will be considered. 



Three species were studied: (1) mice, LAF X genetically homogeneous 

 hybrids, strain A, C-57 black, and C3H, (2) rabbits, crosses of Dutch and 

 American Blue, and (3) guinea pigs, genetically heterogeneous hybrids 

 and inbred strains. 



Groups of the three species of animals were exposed to doses of 0.11, 

 1.1, 2.2, 4.4, or 8.8 r for 8 hours per day for periods extending in some 

 experiments to more than three years. 



Observations on Mice. Male and female LAFi mice received total 

 dosages as high as 5880 r in the 8.8-r exposure group and correspondingly 

 lower at the other exposure levels (Table 16-3). 



The blood data indicate considerable radioresistance of the hemato- 

 poietic system. There was a decrease in all cellular hematologic con- 

 stituents in the peripheral blood of animals exposed to 8.8 r daily. The 

 mean reduction in erythrocyte, hemoglobin, and platelet values was 

 relatively minimal and was not more than 30 per cent at any time. This 

 reduction occurred slowly over a period of seventy-nine weeks. Indi- 

 vidual animals, however, did develop severe anemia. Only a question- 

 able reduction in the erythrocyte or hemoglobin and platelet values 

 occurred in the groups exposed to 4.4 r. No anemia or thrombocytopenia 

 was observed in the groups exposed to 2.2 r and below. 



The mean leukocyte count was reduced in the 8.8-, 4.4-, and 2.2-r 

 groups, but this was a reflection of the lymphocyte reduction. The 

 heterophils remained within control limits. In general, female mice 

 were more radiosensitive than males as far as hematologic findings were 

 concerned. 



Data available on C 3 H and C 3 Hb females and strain A males show that 

 these strains are all comparable to LAFi in respect to their hematologic 

 response to this chronically administered radiation. 



Observations on Female Rabbits. Evidence of irradiation damage to 

 the hematopoietic system was slight even though the highest accumulated 

 dose was approximately 12,000 r. During the first 100 weeks of exposure 

 the total white count of all experimental groups was lowered. The 

 lymphocyte reduction is evident and is made more pronounced by a 

 concomitant relative increase in heterophil values in all exposure groups 

 except those at the 0.1 1-r level. As was observed in mice and guinea 

 pigs, these changes became apparent within the first few weeks after the 



